Since the advent of mountain biking, there has been a perceived need for a bicycle gearing system that both is resistant to being derailed by debris that is accidentally kicked up into the gear set by a bicycle rider and yet offers a wide range of gearing. Toward this goal gearing systems have appeared in the literature, in which the gears are encased in a protective housing.
In these new systems a drive wheel may be co-journalled with a driven set of gears and, in turn, drive a cog wheel on the bicycle's rear wheel. Unfortunately, these systems do not have as wide a range of gearing options as some mountain biking enthusiasts might desire. Moreover, the inner workings of some gear box designs are fairly complicated, resulting in a gear box that is heavier and more prone to larger frictional losses and rapid wear than is desirable.
Moreover, these newer types of bicycle transmissions, in which sprockets are placed in close proximity to each other, do not offer as fast a transition between gears as some bicycle riders prefer. They also typically do not permit a change between gears of more than one gear spacing, for example from third gear to sixth gear. Accordingly, there is a need for a gear assembly that permits faster gear changes and gear skipping during a gear change.